1. Field of the Invention
The present invention generally relates to an image forming apparatus that is provided with image carriers, and in particular to control for cleaning the image carriers.
2. Description of the Related Art
Transfer-system image forming apparatuses that adopt an electrophotographic process, an electrostatic recording process, or the like need to clean a developer that has not transferred to paper and remains on the surface of an image carrier. However, if the image carrier and a cleaning blade are left in contact with each other, finely-powdered toner, an additive agent, and the like aggregate in such a contact area, which causes streaks and image blurring (density fluctuation and the like) to occur. Generally, a friction coefficient μ of the portion of the surface (peripheral surface) of the image carrier on which finely-powdered toner and the like aggregate relatively becomes lower. Thus, the rotational velocity (circumferential velocity) of the image carrier becomes temporarily faster while the cleaning blade is passing the portion in which the friction coefficient μ is low. This is a cause of streaks and image blurring.
According to the invention disclosed in Japanese Patent Laid-Open No. 2005-62280, it has been proposed that an image carrier is stopped when image formation ends, finely-powdered toner is removed by slightly rotating the image carrier thereafter, and toner agglomerate is reduced by further rotating the image carrier in reverse.
With an image forming apparatus that is provided with a plurality of image carriers side by side and forms multicolor images, it is important to match the rotation phases of the image carriers to reduce color misalignment. Color misalignment occurs due to image formation positions (transfer positions) of a plurality of image carriers that respectively correspond to different colors not matching. Japanese Patent Laid-Open No. 2006-330299 has proposed that the phases are aligned after image formation ends such that the phase difference between a plurality of image carriers becomes smaller, and thereafter the image carriers are stopped.
However, Japanese Patent Laid-Open No. 2006-330299 does not take into consideration the cleaning sequence after image formation ends as disclosed in Japanese Patent Laid-Open No. 2005-62280. Specifically, if the cleaning sequence is executed after the phases are aligned, there is a possibility that the phases may shift again. Generally, in the image forming apparatuses that have a plurality of stations, the stations are respectively equipped with a different cartridge. Specifically, since the load on each motor differs depending on the wear state of the cartridges and the difference therebetween, the amount of movement of the surface (peripheral surface) of the carriers will also differ. This also leads to a possibility of increasing the phase difference between the image carriers. Note that the phases may be aligned when the image carriers are started up next time, which will increase a first print-out time.